A bauxite specification sheet is a short document that carries a lot of money. Each line tells you something about how the ore will behave in your plant, and each one can be negotiated. Here is how to read it.
The chemistry lines
Most specs report bauxite chemistry as oxides, in percent by weight, usually on a dry basis.
Al₂O₃ (alumina)
The headline number. Check whether it is total alumina, measured by full chemical analysis, or available alumina, the share that dissolves under defined Bayer digestion conditions. For refineries, available alumina is the figure that pays.
SiO₂ (silica)
Again, ask which kind. Total silica includes quartz, which is largely inert at low digestion temperatures. Reactive silica, mostly from kaolinite clay, is what consumes caustic soda in a refinery. For cement and refractory buyers, total silica matters more. Read why reactive silica matters.
Fe₂O₃ (iron oxide)
Iron gives bauxite its colour. Refineries tolerate a fair amount, though it adds to residue. Refractory makers want it very low, because iron acts as a flux at high temperature. Cement plants want it predictable.
TiO₂ (titania)
Usually present as anatase. Low levels are normal; for refractory grade it is a key limit alongside iron.
LOI (loss on ignition)
The percentage of weight lost when the sample is heated to a high temperature, mostly chemically bound water. Gibbsitic ore has a high LOI, because gibbsite holds more water than boehmite. LOI helps check that the analysis adds up and indicates the mineral form.
Minor elements
Depending on the buyer, specs may also cap CaO, MgO, alkalis (Na₂O, K₂O), P₂O₅, sulphur, organic carbon or other trace elements.
The physical lines
| Line | What it means | Why it matters |
|---|---|---|
| Free moisture | Water held on the surface, not in the minerals | You pay freight on it; high moisture affects handling and shipping safety |
| Size distribution | Percentage passing or retained on set screens | Must suit the buyer's crushers, mills or kilns |
| Lumps vs fines | Share of coarse material vs dust | Fines can cause dust, losses and handling problems |
For sea freight, moisture interacts with shipping rules on cargo safety. See moisture in bauxite.
Typical, guaranteed and rejection limits
Specifications often list three different kinds of number, and confusing them causes disputes.
- Typical values describe the ore on average. They are informative, not binding.
- Guaranteed values are the contractual minimum or maximum for each lot.
- Rejection limits are the points beyond which the buyer can refuse the cargo, as opposed to applying a price adjustment.
Many contracts add price adjustments for alumina above or below the base, and penalties for silica, moisture or other elements outside the band.
The certificate of analysis
A spec sheet says what the ore should be. A certificate of analysis (CoA) says what a particular lot is. When you receive one, check:
- Which lot, stockpile or vessel it covers, and the sampling date.
- Where the sample was taken: at the stockpile, during loading or at discharge.
- The method and the lab, including whether an independent inspector was involved.
- Whether results are on a dry or as-received basis.
At Minequor every lot is sampled twice, at the minehead stockpile and again at loading, so the certificate reflects what actually leaves the site. More in bauxite sampling and quality control.